The present invention generally relates to setting a clock in a cellular telephone. More particularly, the present invention relates to automatically setting a cellular telephone clock to a correct time and date.
Cellular telephones (cell phones) typically have a built-in clock. A cell phone clock can be a hardware component or a software component. Typically, the cell phone clock maintains the current time as the xe2x80x9cdevice time.xe2x80x9d One of the primary functions of a cell phone clock is to provide the current time to a cell phone user. As cell phones have become more sophisticated and more versatile, cell phone users have come to rely on their cell phones to provide an array of functions, such as access to email, short text message transmission, and Internet browsing. Similarly, users have become accustomed to relying on their cell phones for access to the correct time. Unfortunately, a cell phone""s clock can provide the incorrect time for various reasons.
When a cell phone is first used, the clock is not usually correctly set and the user must normally correctly set the clock at least one time. However, like the users of the ubiquitously flashing VCR clock, many cell phone users do not make the effort to correctly set a cell phone clock. A cell phone clock also can provide the incorrect time when the cell phone""s battery is allowed to completely discharge or when the battery is disconnected from the cell phone, thereby permitting the clock to lose the ability to store a correct time. Yet another way that a cell phone clock can provide the incorrect time is when a user simply sets the clock with the wrong time.
Regardless of the method by which the clock becomes incorrectly set, a cell phone user will typically desire that the clock is correctly set, so that the user can rely on the cell phone clock for the correct time. One approach to setting a cell phone clock is to send a time set command as a portion of a control message transmitted from a cellular base station to a cell phone. Some cellular telephone networks have a network feature that transmits a current time to cellular telephones on the network. However, there are many cellular networks that do not provide a specific signal, control message, and/or mechanism for providing a time-set function (e.g., GSM networks and TDMA networks). In such networks, there is a need for an automated feature for providing the current time to a cellular telephone. Therefore, there is a need in the art to enable a cell phone clock to be set automatically, without relying on a specialized command message from the cellular telephone system.
The present invention meets the above-described needs by automatically setting a cell phone device time to match a timestamp contained in a Short Messaging Service (SMS) status report. Accordingly, a cell phone""s clock can be properly set any time the cell phone receives an SMS status report.
SMS messages are short electronic messages that can be transmitted from and to cell phones that operate on a Global System for Mobile Communications (GSM) cellular network. The SMS system allows short text/data messages to be sent and received by cell phones or other cellular devices on the GSM network. A sub-network of Short Messaging Service Centers (SMSCs) functions within the GSM network and provides this service by receiving and routing SMS messages.
In addition to permitting users to send an SMS message to a particular recipient""s cell phone, the SMS architecture enables the sender to request a status report message to be returned. A status report contains information from the SMSC about the status of the short message, for example, whether or not the message was successfully delivered. In addition, the status report contains a time stamp provided by the SMSC, indicating the time at which the status report was generated by the SMSC. The time provided by the SMSC is referred to as the world time, because it indicates a global network time maintained by the SMSCs operating on the GSM network. By setting the cell phone device time to the world time, the clock on the cell phone is automatically set, without requiring any action by the user and without requiring a special time set control message.
When the cell phone transmits the initial SMS message, the cell phone stores the device time corresponding to the time that the message was sent (DTS). When a status report is received, the cell phone stores the device time corresponding to the time that the status report was received (DTR). Additionally, the cell phone stores the world time that is stamped onto the status report by the SMSC that handled the message (WT).
By subtracting the message sent time from the status report received time, the cell phone can determine how long it took, after the short message was transmitted, for the status report to arrive. This difference represents the maximum error in the final device time (DTE) computed from this method. By subtracting the message-received time from the world time, the cell phone can determine an approximate difference between the cell phone""s device time (its clock) and the world time. By adding this difference to the current device time (DTC), the DTC can be set to closely approximate the WT.
In one aspect of the invention, a method is provided for setting a correct time. A status report is received and a world time is determined from the status report. A current device time is set in accordance with the world time.
In another aspect of the invention, a clock for a cellular device is provided. The clock has a current device time for maintaining a current time for the cellular device and a device time difference for maintaining a time difference between the current time and a world time. The clock also has a corrected device time for maintaining the sum of the device time difference and the current device time. The current device time is set equal to the corrected device time, in response to the receipt of the world time; and the world time is received in a status report received by the cellular device.
In yet another aspect of the invention, a cellular telephone is provided. The cellular telephone has a clock operative to provide a displayed time and a radio architecture component operative to receive a status report. The displayed time is set, in response to a receipt of the status report.
The various aspects of the present invention may be more clearly understood and appreciated from a review of the following detailed description of the disclosed embodiments and by reference to the drawings and claims.